1. Field of the Invention
This invention relates to an ink jet recording method and more particularly to an ink jet recording method which comprises applying ink jet recording onto a synthetic pulp paper and then heat-treating the synthetic pulp paper to fuse synthetic pulp and which permits ink recording of high recording density, excellent water resistance, and excellent color reproduction for multi-color recording.
2. Description of the Prior Art
Because of its quietness, fast recording capability, and adaptability to paper of ordinary grade, ink-jet recording is becoming increasingly popular; for example, one application is in computer terminal printers. Furthermore, the ink-jet method can be used to achieve multicolor recording using a plurality of ink nozzles. However, multicolor ink-jet recording involves problems not encountered in monochrome recording. In monochrome recording, one point on a recording paper is subjected to only one recording operation, and therefore satisfactory recording is obtainable most types of paper, e.g., fine paper, rolled paper for payment slips, and papers having greater degree of ink absorption than those previously mentioned. In multicolor recording, ink is squirted from two or more nozzles, and two or more (sometimes four) dots may be merged at one point on the recording paper. Unless the ink drop is absorbed quickly by the layer of paper, it merges with a subsequent ink drop applied on the same point of paper, causing flowing or flying of the ink and smearing thereof on the white background of the paper. If the recorded paper is handled carelessly, its surface may be rubbed to deface the image. Therefore, the use of recording paper having high ink absorption rate is particularly needed in multicolor recording.
Using a recording paper which absorbs ink well, an ink dot generally spreads and at the same time penetrates deep into the paper. For example, paper made as bulky as possible without using a sizing agent absorbs ink very well, and is therefore feasible for use in multicolor ink-jet printing. But the ink dots spread so much on this paper that they give low resolution, and ink penetrates the paper so deep that light scattering due to the interstices in the upper layer of the paper makes the resulting image whitish and less sharp. If four-color (cyan, magenta, yellow and Indian ink) recording is effected on paper of such high ink absorption, the depth of penetration of the first ink dot in the paper is enough to reduce its visibility from above, resulting in poor color reproduction. Pigment-coated paper prepared by coating a pigment and an adhesive on sized paper has low ink absorption properties and cannot be used for multi-color ink jet recording.
As will be understood from the above discussion, to produce an image of high density, resolution and good color reproduction by multicolor ink-jet printing, the following three apparently incompatible requirements must be satisfied: (1) the coloring component of the ink should not show appreciable spreading on the recording paper used; (2) the greater part of said component should remain on the surface of the paper without penetrating deeply into the paper; and (3) the recording paper should have absorbing properties. Several developments have been made in order to achieve such objectives.
As desclosed in Japanese Patent Application (OPI) No. 53012/1977 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application".), when pigment is coated on paper with a low degree of sizing, the major portions of the pigment and the adhesive penetrate into the paper, providing a pigment-filled paper in which the pigment is filled in the pores of the paper. This pigment-filled paper has ink absorption properties and recording density intermediate between the bulky paper containing no sizing agent and the pigment-coated paper. Although the pigment-filled paper has higher ink absorption properties than the pigment-coated paper, they are not sufficient to such an extent that it can be used for multi-color recording. Japanese Patent Application (OPI) No. 49113/78 discloses an ink-jet recording paper wherein paper containing a fine powder of ureaformalin resin is impregnated with a water-soluble polymer. Japanese Patent Application (OPI) No. 74340/77 discloses an ink-jet recording paper having a specified degree of air permeability which absorbs ink in a specified period of time. However, the concept common to these three conventional techniques is to sacrifice ink absorption in order to provide high resolution and density. Although they achieve the intended object to some extent, the resulting paper does not absorb ink well and is not suitable for use in multicolor ink-jet recording. Therefore, there has been a demand in the industry for multicolor ink-jet recording paper satisfying the aforementioned three conditions.
As described above, no ink recording paper has hitherto been obtained which has ink absorption properties suitable for use in multi-color recording and which can provide excellent recording density and color-reproduction.
Forthermore, for conventional ink jet recording papers in which almost no sizing agents are used to improve ink absorption properties, the water resistance of the recording paper is poor, an aqueous ink is generally often used as a recording ink, and the colored recording formed by the ink jet, when moistened with water, runs and elutes, fading in color. Thus they cannot be used for outdoor notification.